Capture error message, otherwise capture cause of HTTP failure (#358)

* Capture error message, otherwise capture cause of HTTP failure

One approach to #356

* Comment to clarify what 'response' might be

Addressing #356 with a comment, since this is a type issue

* Improvement of performance, readability, and priority in failure case

Moving forward on #358 with a bit more aggressive change per discussion

Author: digitalextremist

lib/nano.js

@@ -122,16 +122,18 @@ module.exports = exports = function dbScope (cfg) {
       }
     }
 
-    // let parsed
-    const responseHeaders = Object.assign({
+    const responseHeaders = {
       uri: scrubURL(req.url),
-      statusCode
-    }, response.headers ? response.headers : {})
+      statusCode,
+      ...(response.headers ?? {})
+    };
+  
     if (!response.status) {
-      response.statusText = response.cause.toString()
       log({ err: 'socket', body, headers: responseHeaders })
       if (reject) {
-        reject(new Error(`error happened in your connection. Reason: ${response.statusText}`))
+        // since #relax might have sent Error rather than Response:
+        const statusText = response.cause?.toString() ?? response.message
+        reject(new Error(`error happened in your connection. Reason: ${statusText}`))
       }
       return
     }